Copyright 1999
One of the great joys of telescope making is grinding your own mirror. Now days it is easer to buy finished mirrors than grinding kits to make them. Still grinding your own mirror is a key skill that makes you a real telescope maker.
To grind a telescope mirror by hand you simply attach a glass tool the same size as your mirror blank to the top of a small, strong stand. You apply grinding compounds to the tool and place the mirror blank on top. You then methodically push the mirror blank back and forth while taking small steps around the stand, rotating the blank a little in your hand with each step. If you do this just right, for a number of hours, the mirror will be ground into a section of a perfect sphere.
This stand features a large base that you can walk on. Your weight provides the resistance to your push on the glass so the stand does not need to be either heavily weighted or bolted to the floor like most designs. The central pedestal is small and well under the small top so that you do not have to step around it all the time. The pedestal joints are stiffened with chair leg braces so they do not give very much.
You can adjust the height of the stand and the size of stand top to suit the user and the mirror.
This free design includes two detailed sketches. You can get good copies of them by e-mailing us this little form.
You can make this stand by:
After you download the sketches, these notes will help you understand them more completely.
The front view and top views show the Mirror Grinding Stand with its wide base (big enough to walk around on), pedestal, and small top. The top is only a little bigger than the largest mirror you wish to grind.
The mirror tool is held to the table with three screwed down blocks and six small wedges. This holds it firmly but make it easy to remove.
This sketch is shows the stand parts laid out on a piece of plywood. If you are making only one stand, you can have the sheet cut at 48 inches. This makes it easer to get home.
This small sketch shows a side view of the table top with the tool mounted to it. The mirror is free to move around on top of the tool.
This stand is made from a single sheet of 3/4 inch plywood and bits of wood. The parts are assembled with glue, wood screws, and chair leg braces.
Plywood:
( 23/32 in. thick plywood is OK )
Molding:
Wood Subtotal: $30.50
Hardware Subtotal: $18.50
Finish Subtotal: $ 7.00
This is only an estimate (made in the March 1999). The price may vary in your area. You can save a lot of money if you use a lot of scrap wood. In fact, there is not reason the whole thing can not be made form old pallets and plywood shipping boxes. If you have scrap wood for the pedestals you can make to bases and two table tops from one sheet of plywood.
This stand was designed to be build using a few simple tool.
You will also need sand paper, paint brushes. etc. It would be nice to have a four-in-hand rasp.
This is your stand and you can build it to suit your likes and needs.
You need to decide on these options before you build the stand.
The height of the work should be about the height of the point on the worker's pelvis. This point is easily felt on you side. The pedestal is shown at 36 inches which is about right for a grown man but it may need to be shorter for students.
The table top should be about 2 inches in diameter larger than the diameter of the largest mirror you wish to grind on it. The largest mirror that an experienced person can grind by hand is 12.5 inches. For large mirrors you may want to make the pedestal boards a little wider too.
If you want to make two stands out of one piece of plywood, do not have it cut at the store. The tops have to be made out of the triangular scraps between the bases.
The large circle for the base can be cut with a jig say or a band say. If all you have is a skill saw with a plywood blade or a hand saw, you can make the base an octagon.
The top is made the same way but it is smaller and it really should be round.
Glue and nail the 1-by-4 pieces to the 2-by-2 core. Be very careful that the ends of all the pieces are flat and square. The 2-by-2 is not important for strength, so you can use just a couple blocks to help hold the sides in place for nailing.
The pedestal must be centered on the top and base and firmly secured. These stands are awkward to store so it is best if you do not glue the pedestal to the base. It can then be removed for storage.
Be sure that the ends of the pedestal are even and square. It is important the pedestal be square both ways to the top and base.
Screws installed down through the top into the end grain of the pedestal do not hold very well. Likewise glue on the end grain does not hold. This design address this problem by using 1 inch chair leg braces. These pieces of hardware are usually sold in sets of four and are very strong. Be sure to mark the screw holes with the awl and drill pilot holes.
You could same a little money by using 16 scrap blocks of hardwood instead. These would have to be attached with screws and glue everywhere except on the base.
In normal use, the top is covered with several layers of newspaper cut a bit larger than the top. The blocks are then screwed down through the paper placed for a loose fit on the tool. The tool is then held by taping a wedge in each direction at each block.
Regularly you remove the tool and clean it. Every time you change grits, you remove the blocks and replace the newspaper. This very important to help control stray grit.
The tool is typically only a .5 inch thick piece of float glass, so the blocks cannot be very tall. You do not want the mirror blank to touch the blocks. The blocks are held down with two #8 wood screws but no glue.
I made my wedges from thin hardwood scrap. Basically I used Popsicle sticks made of maple and sanded them to be a wedge.
You may finish your stand any way you like but the plywood should be sealed against water. The grits are used with water to remove the cut glass and this water gets split over the top and base. We recommend:
Plywood edges take some effort to seal. The end result should be uniform in texture and not have holes one place and excess filler another.
First fill all visible holes with glue and wood splinters. Toothpicks work well. Let dry and sand with course paper over a wooden block. Fill with wood putty (I like the powder you mix with water). Let this dry thoroughly and sand again. Seal with a thinned coat of shellac. Sand again and refill. Sand again, seal again, and sand with fine sand paper. In the process you can round the edges of the plywood a little bit. The edges are now ready to be painted.
Priming the wood with thinned shellac help seal the wood, and helps the paint both to stick and to cover more area.
Two coats of oil based enamel should last for many years except where you walk.
All that is left is to reassemble the stand, and install the tool. Screw the pedestal back to the base. Place the tool in the center of the top and drill pilot holes for the block screws.
Cover the top with several layers of newspaper and find the block pilot holes with an awl. Screw down the blocks and secure the tool with the wedges.
Thanks again for using a Woodware Computer Plan. We very much want to know how you are getting along with your project and would be happy to answer any questions by email.
If you send us a picture of your finished stand, we would be happy to put it on our web page. We need pictures of finished projects with real people standing beside them
.